As dissolved by U.S. Pat. No. 4,547,342 and FIG. 11, the gas generator that has been generally used, comprises a housing 1 with an upper container body 2 and a lower container body 3. The upper container body 2 has an inner cylinder wall 4 and an outer cylinder wall 6 with an intermediate cylinder wall 5 there-between and the lower container body 3 has faces which are butted on the lower end portions of the cylinder walls respectively and friction-welded so that the upper container body 2 and the lower container body 3 may become into a unit. An ignition chamber 7 is formed inside the inner cylinder wall 4 in the housing 1. A combustion chamber G is formed between the inner cylinder wall 4 and the intermediate cylinder wall 5. A filter chamber F is formed between the intermediate cylinder wall 5 and the outer cylinder wall 6. And the inner cylinder wall 4 is provided with first gas holes 4a, the intermediate cylinder wall 5 is provided with second gas holes 5a and the outer cylinder wall 6 is provided with gas release holes 6a. In the ignition chamber 7, an igniter 9 and enhancer 10 are placed. Inside the combustion chamber G, gas generating agent 11 and a first filter 12 are arranged in the radial direction in that order. In the filter chamber F, a regulation plate 13 and second and third filters 14, 15 are mounted in that order. The regulation plate 13 is bent at its upper end to contact with the upper inner surface of the container 1 and seal the upper portion, and has a gas holes 13a so that the gas from the combustion chamber G is led downward along the regulation plate 13 into the filter chamber F through the gas hole 13a.
Upon crash of a motor vehicle, the sensor detects the impact and sends an activate signal to an electric detonator taking a roll of an igniter 9.
Then, the enhancer 10 is ignited by the flame from the igniter 9. Large quantity of heat particle current is generated by the enhancer 10 in turn flows into the combustion chamber G through the first gas holes 4a (as indicated by an arrow in the drawing) and fires the gas generating agent 11. The gas generating agent bursts out into flame then high-temperature gas containing slug is produced. This gas cools down during passing through the first filter 12, then flows into the filter chamber F through the second gas holes 5a and goes downward along the regulation plate 13. The gas then passes through the gas holes 13a and goes upward along the second filter 14, and passes through the second filter 14 and the third filter 15 while the gas is cooled and cleared of slug. Lastly, the gas becomes clear with a proper temperature and is discharged into the air bag (not shown in the drawing) through the gas release hole 6a.
The enhancer 10 used in the aforesaid gas generator takes a roll of a combustion improver to fire the gas generating agent 11, which is basically different from the gas generating agent 11.
There is boron niter (BKNO.sub.3) as one of the enhancers, which have been generally used. It is considered that a process of transfering fire proceeds as follows. The gasification percentage of boron niter is about 10 percent. Therefore, when the igniter 9 ignites boron niter, the heated metal oxide particles are dispersed into the combustion chamber G with a generated heated gas current. Then, the heated metal oxide particles stick on the surface of the gas generating agent 11. The gas generating agent 11 starts to burn at the struck spots. When the gas generating agent 11 is an organic type (so-called a non-azide type), the stuck spots, in other words, the heated areas of the gas generating agent, are firstly softened and melted then vaporized. Consequently, combustion reaction are started at the stuck spots. Further, at the portions surrounding the the stuck spots, combustion reactions are successively occurred by combustion heat from the the stuck spots in the same manner. Thus, the combustion reaction broadens rapidly.
The combustion of the gas generating agent at an initial stage can be regarded as local combustions at the spots on which the heated boron particles stick. Therefore, in order to increase the initial firing area of the gas generating agent, it is suggested to assure making space among of pellets of the gas generting agent so as to increase area on which the heated boron particles stick. The space among of the gas generating agent pellets plays a roll of a passage for the heated boron particles passing through. However, according to this way, the packing percentage of the gas generating agent pellets decreases and a larger size gas generator is required. This is contrary to the trend of size and weight reductions.
Also, when the packing density of the gas generating agent is raised so as to reduce size and weight of the gas generator, it is difficult for the heated boron to stick to the pellets of the gas generating agent uniformly and it hard to adjust the combustion velocity.
Further, when a car which has met with no accident, is treated to abandon, the gas generator is remove from an air bag module and incinerated since it is difficult to pick up the only gas generating agent from the air bag module. While the incineration of the gas generator, the housing of the gas generator is heated and becomes so brittle. In this time, the gas generator may explode and break because of combution of the gas generating agent, which can bring danger to the neighboring area. Also, this kind of danger may occur in other case than the incineration, for example, when a car catches fire at accident other than a collision. Therefore, nowadays, such spontaneous firing explosive as shown in U.S. Pat. No. 4,561,675 is proposed in order to preclude the above danger. The spontaneous firing explosive is dispoed inside the housing of the gas generator to separate from the gas generating agent and the enhancer, and is spontaneously fired before the housing deterioration due to high temperature. In other words, the spontaneous firing explosive is spontaneously fired at one temperature which is lower than another temperature at which the housing deteriorates. In placed of the igniter 9, the spontaneous firing explosive ignites the gas generating agent in the gs generator. However, this method has a problem that the fourth material like a spontaneous firing explosive is needed in addition to the gas generating agent, the enhancer and the igniter. The gas generating agent, the enhancer and the spontaneous firing explosive have different compositions respectively. Therefore, in order to produce the prior gas generator, process and factory must be provided to each of the gas generating agent, the enhancer and the spontaneous firing explosive although applied quantities of the enhancer and the spontaneous firing explosive are a very little in comparison with the gas generating agent. This is one of reasons of increasing a cost for producing the gas generator.
The present invention aims to solve the above said problems involved in the known gas generator including the above-mentioned known gas generating agent and enhancer. Specifically, the first aim of the present invention is providing enhancer having a function of spontaneously firing at a temperature which is lower than another temperature at which the housing of the gas generator deteriorates. The second aim of the present invention is provided an enhancer which enables a gas generating agent, especially having an organic type fuel as main ingredient, to ignite uniformly. The third aim of the present invention is providing enhancer of which composition can be also employed as a gas generating agent.
In other words, when an explosive composition having a function of spontaneously firing at a temperature which is lower than another temperature at which the housing of the gas generator deteriorates, is employed as an enhancer, further, when the spontaneous firing explosive composition is employed as a gas generating agent, it is not necessary to provide with different facilities respectively for producing the enhancer, the spontaneous firing explosive composition and the gas generating agent. Whereby, an inexpensive gas generator can be provided. In these views, intensive research and development work have been undertaken and resulted in the present invention which is disclosed hereinafter.